1. Field of the Invention
Embodiments of the present invention relate to a liquid crystal display device (LCD), and more particularly, to a substrate for the LCD and a method of fabricating the same. Although embodiments of the invention are suitable for a wide scope of applications, it is particularly suitable for preventing light leakage using a light shielding means that is not a black matrix formed by a photolithography process.
2. Discussion of the Related Art
Generally, an LCD device uses optical anisotropy and polarization properties of liquid crystal molecules to display an image. The liquid crystal molecules have an alignment direction along their thin and long shapes. The alignment directions of the liquid crystal molecules can be controlled by applying an electric field to the liquid crystal molecules. In other words, as the intensity of the electric field is changed, the orientation of the alignment direction for the liquid crystal molecules also changes. Since incident light through liquid crystal molecules is refracted based on the orientation of the liquid crystal molecules, due to the optical anisotropy of the aligned liquid crystal molecules, intensity of the incident light can be controlled such that images can be displayed.
Among the various types of LCD devices commonly used, active matrix LCD (AM-LCD) devices having thin film transistors (TFTs) with pixel electrodes connected to the TFTs disposed in matrix form have high resolution and superiority in displaying moving images.
FIG. 1 is a schematic perspective view of an active matrix liquid crystal display device according to the related art. As shown in FIG. 1, an array substrate 10 and a color filter substrate 20 face each other, and a layer of liquid crystal molecules 30 is interposed between the array substrate 10 and the color filter substrate 20. The array substrate 10 includes a first transparent substrate 12, a plurality of gate lines 14 and a plurality of data lines 16 crossing each other. Each of the plurality of gate lines 14 and each of the data lines 16 cross each other to define pixel regions “P.” A thin film transistor “T” is formed at a crossing of the gate line 14 and the data line 16, and a pixel electrode 18 is connected to the thin film transistor “T” and is disposed in the pixel region “P.” The color filter substrate 20 includes a second transparent substrate 22 including the pixel region “P,” a black matrix 25 surrounding the pixel region “P” and disposed on an inner surface of the second transparent substrate 22, a color filter layer 26 including red, green and blue sub-color filters 26a, 26b and 26c and disposed within the black matrix 25. More specifically, the red, green and blue sub-color filters 26a, 26b and 26c are disposed in each pixel regions “P” and boundaries between the red, green and blue sub-color filters 26a, 26b and 26c correspond to the black matrix 25. A common electrode 28 is disposed on the color filter layer 26.
Although not shown, a seal pattern (not shown) of sealant is interposed between the array substrate 10 and the color filter substrate 20 at a periphery of the array substrate 10 and the color filter substrate 20 to attach the array substrate 10 to the color filter substrate 20 and to prevent leakage of the liquid crystal molecules 30. Further, a first orientation film (not shown) is formed between the pixel electrode 18 and the layer of liquid crystal molecules 30, and a second orientation film (not shown) is formed between the common electrode 28 and the layer of liquid crystal molecules 30. Here, the first and second orientation films set an initial direction of sub-layers of liquid crystal molecules within the layer of liquid crystal molecules 30. Furthermore, first and second polarizers (not shown) are disposed at outer surfaces of the first and second transparent substrates 12 and 22, respectively. Additionally, a backlight (not shown) is disposed at a backside of the first polarizer to supply a light source to the LCD.
When on/off signals of the thin film transistor “T” are sequentially scanned into the gate lines 14 and image signals of the data lines 16 are transmitted to the pixel electrode 18, the liquid crystal molecules 30 are driven by a vertical field electricity generated between the common electrode 28 and the pixel electrode 18. Therefore, various images can be displayed in accordance with the change of the transmittance.
The above-mentioned LCD is manufactured through an array process including forming the thin film transistor “T” and forming the pixel electrode 18 connected to the thin film transistor “T” and through a color filter process including forming the color filter layer 26 and forming the common electrode 28.
FIGS. 2A to 2G are schematic cross-sectional views illustrating a method of fabricating a color filter substrate according to the related art. As shown in FIG. 2A, a black matrix material layer 62 is formed by depositing a metallic material, including a chromium (Cr) on a transparent substrate 60. Next, a photoresist layer 64 is formed by coating a photoresist on the black matrix material layer 62. A mask 66 having a transmission area “TA” and a blocking area “BA” is disposed on the photoresist layer 64, and the photoresist layer 64 is exposed using the mask 66.
Next, as shown in FIG. 2B, a photoresist pattern 68 is formed by developing the exposed photoresist layer 64. The photoresist pattern 68 is disposed on the black matrix material layer 62 to correspond to a portion where a black matrix is to be formed later.
As shown in FIG. 2C, a black matrix 72 having first to third openings 70a, 70b and 70c is formed by removing a portion of the black matrix material layer 62 exposed by the photoresist layer 64. Although not shown, the black matrix 72 has a lattice shape in a plan view.
Next, as shown in FIG. 2D, a portion of the photoresist pattern 68 that remains on a top surface of the black matrix 72 is removed by stripping. For example, a red resist layer 74a is formed by coating a red resist in the first opening 70a of the black matrix 72. After a mask (not shown) including a transmission area (not shown) and a blocking area (not shown) is disposed on the red resist layer (not shown). The portion of the red resist layer that is to remain in the first opening 70a corresponds to the transmission area. The portion of the red resist layer corresponding to the blocking area is removed because ultra-violet light is blocked through the blocking area. Consequently, a red sub-color filter 74a is formed to correspond to the first opening 70a. Edges of the red sub-color filter 74a overlap the black matrix 72.
Next, as shown in FIG. 2E, green and blue sub-color filters 74b and 74c are sequentially formed by coating and patterning green and blue resists in the second and third openings 70b and 70c using the same process as that of the red sub-color filter 74a. The red, green and blue sub-color filters 74a, 74b and 74c constitute a color filter layer 74.
As shown in FIG. 2F, an overcoat layer 76 is formed by depositing an organic insulating layer on the color filter layer 74. Because a step difference occurs where the color filter layer 74 overlaps the black matrix 72, the overcoat layer 76 is formed to provide a planar surface for the later formed common electrode 78.
As shown in FIG. 2G, the common electrode 78 is formed by depositing a transparent conductive material, such as indium tin oxide (ITO) or indium zinc oxide (IZO) on the overcoat layer 76.
The black matrix 72 according to the related art is manufactured by a photolithography process using a mask, thereby increasing process time and cost. When the black matrix 72 and the color filter 74 are manufactured on the same substrate 60 as explained above, at least four mask processes are necessary to form the black matrix 72 and the color filter layer 74, including the red, green and blue sub-color filters 74a, 74b and 74c, thereby increasing the length and complexity of the manufacturing process so as to reduce productivity. Further, because the mask in the mask process has a relatively high-cost, the manufacturing cost is increased when the number of masking processes are increased.
To remove the step differences of the red, green and blue sub-color filters, the overcoat layer should be formed to provide a planar surface for the subsequent formation of the common electrode. Therefore, the productivity is reduced because of the need for a planarization overcoat layer. Further, the black matrix material in the pixel region may not be completely removed from the transparent substrate after forming the black matrix, so a black defect may occur. Product yield is reduced by such a black defect.